Electrolyte for removing titanium-containing coatings and removing method using same

ABSTRACT

An electrolyte for removing titanium-containing coatings from substrates is provided. The electrolyte includes alkali, accelerant, and inhibiter. The alkali is hydroxide. The accelerant is a complexant capable of complexing with titanium. The inhibiter is polyphosphate. A method for removing titanium-containing coatings from substrates is also described there.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is one of the five related co-pending U.S. patent applications listed below. All listed applications have the same assignee. The disclosure of each of the listed applications is incorporated by reference into all the other listed applications.

Attorney Docket No. Title Inventors US 33408 ELECTROLYTE FOR REMOVING WEI HUANG TITANIUM-CONTAINING COATINGS et al. AND REMOVING METHOD USING SAME US 33410 SOLUTION FOR REMOVING TITANIUM- WEI HUANG CONTAINING COATINGS AND et al. REMOVING METHOD USING SAME US 33411 SOLUTION FOR REMOVING TITANIUM- WEI HUANG CONTAINING COATINGS AND METHOD et al. FOR SAME US 33412 SOLUTION FOR ELECTROLYTICALLY WEI HUANG REMOVING CHROMIUM CARBIDE et al. COATING AND METHOD FOR SAME US 33413 SOLUTION SYSTEM FOR ELECTRO- WEI HUANG LYTICALLY REMOVING TITANIUM et al. CARBIDE COATING AND METHOD FOR SAME

BACKGROUND

1. Technical Field

The present disclosure relates to an electrolyte for removing titanium-containing coatings and a method for removing such coatings.

2. Description of Related Art

Hard titanium containing coatings, such as titanium nitride and titanium carbide, impart specific properties to workpieces such as machining tools, die core-pins, and high temperature devices. These hard coatings resist wear, abrasion, oxidation, and corrosion, and reduce susceptibility to chemical reactions with the workpieces to which they are applied. These coatings, however, can fail locally during manufacture or use.

When the coatings fail, the entire die or tool component is discarded even if the underlying substrate shows no damage, at considerable cost. For this reason, the ability to recycle the underlying substrate by removing a failed coating and replacing it with a new coating is economically preferable.

Therefore, there is room for improvement within the art.

DETAILED DESCRIPTION

The present disclosure relates to an electrolyte and a related method for removing titanium-containing coatings formed on the surfaces of substrates. The titanium-containing coatings may be titanium nitride coatings, titanium carbide coatings, titanium aluminum nitride coatings, or other titanium containing coatings. The substrate may be made of stainless steel or ferric-based alloy.

The electrolyte may be an aqueous solution containing alkali, accelerant, assistant agent, and inhibiter.

The alkali may be hydroxide, such as sodium hydroxide, potassium hydroxide, or a combination thereof. In this exemplary embodiment, sodium hydroxide may be selected. The concentration of the alkali may be about 10-300 g/L, and in this exemplary embodiment is about 20-200 g/L. The alkali provides an alkali condition for the titanium contained in the coatings to change to titanium ions during electrolysis process.

The accelerant may be a complexant capable of complexing with titanium, such as sodium potassium tartrate, sodium gluconate, sodium citrate, edetic acid (EDTA), or a combination thereof. The concentration of the accelerant selected may be about 5-150 g/L, and in this exemplary embodiment is about 20-100 g/L. The accelerant acts with the metallic ions of the titanium-containing coating and speeds dissolution of the titanium-containing coatings into the electrolyte.

The assistant agent may be alcohol amino, such as ethanolamine, diethanolamine, triethanolamine, or a combination thereof. The concentration of the assistant agent selected may be about 5-80 ml/L, and in this exemplary embodiment is about 10-50 ml/L. The assistant agent can diminish the tension of the electrolyte, facilitate the penetration of the action ions into the coatings, and accelerate dissolving of the coatings.

The inhibiter may be polyphosphate, such as sodium tripolyphosphate, sodium pentapolyphosphate, or a combination thereof. The concentration of the inhibiter selected may be about 0.5-10 g/L, and in this exemplary embodiment is about 2-8 g/L. The inhibiter protects the substrate from being etched or damaged by the alkali.

The electrolyte may be prepared by dissolving the alkali, accelerant, assistant agents, and inhibiter in water.

The method for removing the titanium-containing coating formed on the substrate may include steps of providing the electrolyte, immersing the substrate having the titanium-containing coating in the electrolyte, with the substrate electrified and acting as an anode to remove the coating. Carbon material may be used as the cathode during the electrolysis. The electrolyte may have a temperature of about 50-95° C. The electric current density through the electrolyte is about 1-10 A/dm², and in this exemplary embodiment is about 4-7 A/dm². After electrolysis, the substrate may be rinsed with water and dried. The coating can be effectively removed from the substrate and the underlying substrate is free from damage by the present method.

EXAMPLES

Experimental examples of the present disclosure follow:

Example 1

40 grams (g) sodium hydroxide, 40 g sodium potassium tartrate, 30 g sodium citrate, 40 g EDTA acid, 3 g sodium pentapolyphosphate, and 60 ml triethanolamine were added to deionized water to produce 1000 ml of electrolyte. The electrolyte was then heated to about 70° C.

Samples of stainless steel substrate were provided. The stainless steel substrate samples had titanium aluminum nitride coatings formed thereon. The samples, being anodes, were completely immersed in the electrolyte for about 10 minutes at an electric current density of about 5 A/dm². After electrolysis, the samples were taken out of the electrolyte and were dried after being rinsed with water.

The samples processed were inspected by X-ray diffraction (X-RD). No titanium and aluminum were detected on surfaces of the samples. Accordingly, the coatings were effectively and completely removed from the stainless steel substrate. Furthermore, the processed samples were scanned using scanning electron microscopy. The scanning found no damage to the stainless steel substrate.

Example 2

80 g sodium hydroxide, 30 g sodium potassium tartrate, 60 g sodium citrate, 50 g edetic acid, 8 g sodium pentapolyphosphate, and 20 ml triethanolamine were added to deionized water to produce 1000 ml of electrolyte. The electrolyte was then heated to about 90° C.

Samples of stainless steel substrate were provided. The stainless steel substrate samples had titanium carbide coatings formed thereon. The samples, being anodes, were completely immersed in the electrolyte for about 12 minutes at an electric current density of about 6 A/dm². After electrolysis, the samples were taken out of the electrolyte and were dried after being rinsed with water.

The samples processed were inspected by X-ray diffraction (X-RD). No titanium was detected on surfaces of the samples. Accordingly, the coatings were effectively and completely removed from the stainless steel substrate. Furthermore, the processed samples were scanned using scanning electron microscopy. The scanning found no damage to the stainless steel substrate.

Example 3

50 g sodium hydroxide, 20 g sodium potassium tartrate, 2 g sodium tripolyphosphate, and 25 ml diethanolamine were added to deionized water to produce 1000 ml of electrolyte. The electrolyte was then heated to about 85° C.

Samples of stainless steel substrate were provided. The stainless steel substrate samples had titanium nitride coatings formed thereon. The samples, being anodes, were completely immersed in the electrolyte for about 14 minutes at an electric current density of about 7 A/dm². After electrolysis, the samples were taken out of the electrolyte and were dried after being rinsed with water.

The samples processed were inspected by X-ray diffraction (X-RD). No titanium was detected on surfaces of the samples. Accordingly, the coatings were effectively and completely removed from the stainless steel substrate. Furthermore, the processed samples were scanned using scanning electron microscopy. The scanning found no damage to the stainless steel substrate.

Example 4

10 g sodium hydroxide, 30 g sodium potassium tartrate, 30 g sodium gluconate, 20 g edetic acid, 0.5 g sodium pentapolyphosphate, and 80 ml triethanolamine were added to deionized water to produce 1000 ml of electrolyte. The electrolyte was then heated to about 60° C.

Samples of ferric-based alloy substrate were provided. The ferric-based alloy substrate samples had titanium carbide coatings formed thereon. The samples, being anodes, were completely immersed in the electrolyte for about 12 minutes at an electric current density of about 6 A/dm². After electrolysis, the samples were taken out of the electrolyte and were dried after being rinsed with water.

The samples processed were inspected by X-ray diffraction (X-RD). No titanium was detected on surfaces of the samples. Accordingly, the coatings were effectively and completely removed from the ferric-based alloy substrate. Furthermore, the processed samples were scanned using scanning electron microscopy. The scanning found no damage to the ferric-based alloy substrate.

Example 5

300 g potassium hydroxide, 5 g sodium potassium tartrate, 10 g sodium pentapolyphosphate, and 5 ml ethanolamine were added to deionized water to produce 1000 ml of electrolyte. The electrolyte was then heated to about 75° C.

Samples of stainless steel substrate were provided. The stainless steel substrate samples had titanium carbide coatings formed thereon. The samples, being anodes, were completely immersed in the electrolyte for about 15 minutes at an electric current density of about 6 A/dm². After electrolysis, the samples were taken out of the electrolyte and were dried after being rinsed with water.

The samples processed were inspected by X-ray diffraction (X-RD). No titanium was detected on surfaces of the samples. Accordingly, the coatings were effectively and completely removed from the stainless steel substrate. Furthermore, the processed samples were scanned using scanning electron microscopy. The scanning found no damage to the stainless steel substrate.

It is believed that the present embodiment and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its advantages, the examples hereinbefore described merely being preferred or exemplary embodiment of the disclosure. 

1. An electrolyte for removing titanium-containing coatings from substrates, comprising: an alkali, the alkali being hydroxide; an accelerant, the accelerant being a complexant capable of complexing with titanium; and an inhibiter, the inhibiter being polyphosphate.
 2. The electrolyte as claimed in claim 1, wherein the hydroxide is sodium hydroxide, potassium hydroxide, or a combination thereof.
 3. The electrolyte as claimed in claim 2, wherein the hydroxide has a concentration of about 10-300 g/L.
 4. The electrolyte as claimed in claim 2, wherein the hydroxide has a concentration of about 20-200 g/L.
 5. The electrolyte as claimed in claim 1, wherein the complexant comprises one or more of the group consisting of sodium potassium tartrate, sodium gluconate, sodium citrate, and edetic acid.
 6. The electrolyte as claimed in claim 5, wherein the complexant has a concentration of about 5-150 g/L.
 7. The electrolyte as claimed in claim 5, wherein the complexant has a concentration of about 20-100 g/L.
 8. The electrolyte as claimed in claim 1, wherein the polyphosphate is sodium tripolyphosphate, sodium pentapolyphosphate, or a combination thereof.
 9. The electrolyte as claimed in claim 8, wherein the polyphosphate has a concentration of about 0.5-10 g/L.
 10. The electrolyte as claimed in claim 8, wherein the polyphosphate has a concentration of about 2-8 g/L.
 11. The electrolyte as claimed in claim 1, wherein the electrolyte further comprises alcohol amino assistant agents selected from one or more of a group consisting of ethanolamine, diethanolamine, and triethanolamine.
 12. The electrolyte as claimed in claim 11, wherein the alcohol amino has a concentration of about 5-80 ml/L.
 13. The electrolyte as claimed in claim 11, wherein the alcohol amino has a concentration of about 10-50 ml/L.
 14. A method for removing titanium-containing coatings from substrates, comprising: providing an electrolyte, the electrolyte containing alkali, accelerant, and inhibiter; immersing the substrate with the titanium-containing coating in the electrolyte, the substrate being an anode; and electrifying the substrate to remove the titanium-containing coatings; wherein the alkali is hydroxide; the accelerant is a complexant capable of complexing with titanium; and the inhibiter is polyphosphate.
 15. The method as claimed in claim 14, wherein the hydroxide is sodium hydroxide, potassium hydroxide, or a combination thereof.
 16. The method as claimed in claim 14, wherein the complexant comprises one or more of the group consisting of sodium potassium tartrate, sodium gluconate, sodium citrate, and edetic acid.
 17. The method as claimed in claim 14, wherein the polyphosphate is sodium tripolyphosphate, sodium pentapolyphosphate, or a combination thereof.
 18. The method as claimed in claim 14, wherein the electrolyte further comprises alcohol amino assistant agents selected from one or more of a group consisting of ethanolamine, diethanolamine, and triethanolamine.
 19. The method as claimed in claim 14, wherein the electrolyte has a temperature of about 50-95° C. and has an electric current density of about 1-10 A/dm² during the removing of the coating.
 20. The method as claimed in claim 14, wherein the substrate is made of stainless steel or ferric-based alloy, and the titanium-containing coating is titanium aluminum nitride coating, titanium carbide coating, titanium nitride, or other titanium containing coating. 